Sitting in the 1902 State Landau in pride of place next to the Queen, the Duchess of Cornwall beamed as she waved to the crowds on the way to Buckingham Palace.

Her key role at the Diamond Jubilee celebrations underlined the amazing transformation of the woman who was once reviled by the public and seen by some royal courtiers as the woman who broke up Charles and Diana’s marriage.

For years she was the “other woman”, but yesterday Camilla’s increased prominence demonstrated she has been truly accepted as part of the Windsors’ future in the Queen’s new slimmed-down version of the Royal Family.

Her Majesty’s decision to have Camilla sitting in the Landau’s seat in the absence of Prince Philip, who was suddenly taken ill, emphatically told the country her daughter in law is now an important part of “The Firm”.

This was reaffirmed by Camilla’s appearance on the Buckingham Palace balcony with the Queen, Charles, William, Kate and Harry just a few moments later, as well as her seat just one along from the Queen in the royal box during Monday’s rock extravaganza.

Only 10 years ago she attended the Golden Jubilee Party at the palace and sat in the background behind the Royal Family trying not to ignite controversy over her relationship with the heir to the throne.

Inner circle: Camilla part of the slimmed-down Royal Family (Image: Getty)

A royal source said: “The jubilee celebrations not only recognised the Queen’s magnificent 60 years on the throne, they also marked the start of a new era for Britain’s Royal Family – with Prince Charles and Camilla at the forefront.

“Prince Philip’s absence on the Buckingham Palace balcony yesterday added to the sense that times are changing rapidly for the monarchy.

“The rest of the royals kept a low profile, and that is how Prince Charles sees the way forward. with Camilla at his side.

“For more than a decade he has privately lobbied for a ‘slimmed down’ monarchy, painfully aware that in hard times the public will not accept a bloated institution at the taxpayers’ expense.”

Today, at a time when the Royal Family is basking in popularity on the world stage, Camilla’s continued appearances as the Queen’s right-hand woman is a PR triumph for those in the palace who intend that she will one day be Queen.

The royal source added: “Camilla has proved herself by taking on royal engagements in the last two or three years successfully enough that her future as a Queen seems more assured.

“Gone are the days when Diana fans pelted her with bread rolls in a car park, after blaming her for breaking up Charles’s marriage to Diana.”

Until now it has generally been accepted Camilla will take on the, albeit unprecedented, title of Princess Consort when Prince Charles becomes King.

Camilla is reported to prefer this title, saying she doesn’t want to be Queen.

But Charles has other ideas, which were revealed in an interview in November 2010 when he was asked if Camilla would be his Queen.

He replied: “That could be.”

Together again: With the Queen and Kate at the river pageant (Image: Kent Gavin / Daily Mirror)

History tells us anything can happen when the Windsors need to navigate their way around tradition and protocol to achieve their goals.

When Charles wanted to marry Camilla in 2005, his position as the future Supreme Governor of the Church of England meant he officially had to ask for permission from the Queen and Parliament.

There are those who believe that had there been fewer constraints on Charles, Camilla may have become his first wife – as she was also his first love.

Instead, he was encouraged to marry the 20-year-old Lady Diana Spencer who came from one of the country’s leading aristocratic families.

Charles and Camilla met in 1970 and were pictured talking during a break in a Windsor polo match sparking rumours of a romance.

There was no proposal and when Charles was posted on overseas naval duties Camilla married army officer Andrew Parker-Bowles in 1973.

A year later she gave birth to Tom and Charles became his godfather. Her daughter Laura was born in 1978.

Camilla and Brigadier Parker-Bowles have six grandchildren including four-year-old Eliza, who was a bridesmaid at Kate and William’s wedding.

The Camilla factor hung heavily over the marriage of Charles and Diana from its beginnings in 1981.

When Charles and Diana were on their honeymoon on the Royal Yacht Britannia in the Mediterranean she discovered that he was wearing cufflinks from Camilla engraved with a double C.

In an interview with Martin Bashir for a special Panorama programme, Diana revealed: “There were three of us in the marriage, so it was a bit crowded.”

Accepted: Royal Family merchandise featuring Camilla (Image: Getty)

To the horror of palace courtiers this was later confirmed by Charles when he admitted having an affair with Camilla, during an interview with Jonathan Dimbleby for documentary The Prince of Wales – The Private Man.

During the mid to late 90s, courtiers gradually tried to introduce the idea of Charles and Camilla as a couple.

But after Diana was killed in 1997 Camilla became public enemy number one and she retreated from public life.

All this makes the transformation of the past 15 years even more incredible.

One source said: “Following the jubilee celebrations the Queen and the Duke will surely scale down their workload, meaning Charles and Camilla will be even more visible.

“Despite the extraordinary stamina of the Queen and the Duke they are after all human beings, as Philip’s recent health scares have proved.

“The Queen has looked happy and content in recent years because she knows the future of the monarchy is now in good hands both with Charles and William.

“All she needs now is her beloved husband back at her side so that she can truly savour her extraordinary achievements.”

The inclusion of Camilla as one of the “key seven” players in the Diamond Jubilee celebrations comes at the end of a rollercoaster ride for her relationship with Charles – but shows they are entering their next phase as an established royal couple.